1. Field of the Invention
The invention relates to a variable massage drive unit for a chair-type massage apparatus, more particularly to a variable massage drive unit having one-way clutches for driving selectively alternate gear sets of the massage drive unit.
2. Description of the Related Art
A known variable massage apparatus, which is mountable on the backrest of a chair, comprises a flat horizontal platform, a vertically extending guide unit mounted perpendicularly on the platform, and a massage drive unit mounted slidably on the guide unit. The massage drive unit includes a hollow casing, a rotatable drive shaft which is disposed uprightly in the hollow casing and which has two end portions that extend out of the hollow casing, upper and lower bearings for mounting rotatably and respectively the end portions of the drive shaft to top and bottom walls of the hollow casing so as to permit rotation of the drive shaft in two opposite revolving directions, and parallel first and second output shafts which are disposed transversely in the hollow casing and which have two end portions that extend out of the hollow casing and that are mounted rotatably to opposite side walls of the hollow casing. The massage drive unit further includes first and second gear sets, each of which has a drive gear disposed coaxially on the drive shaft, and a driven gear meshing with the drive gear and connected rigidly to a respective one of the first and second output shafts. A tubular sleeve is provided around an intermediate portion of the drive shaft between the drive gears of the first and second gear sets. Fastening members are disposed on two ends of the tubular sleeve and retain the latter on the drive shaft. First and second one-way clutches are provided coaxially on the drive shaft between the drive shaft and the drive gear of a respective one of the first and second gear sets. The first and second one-way clutches are operable respectively to the opposite revolving directions and engage selectively the drive gear of one of the first and second gear sets with the drive shaft depending on the direction of rotation of the latter. A linkage unit is mounted pivotally to the end portions of the first and second output shafts on one end and has a massaging wheel unit mounted rotatably on the other end.
For the first gear set, the gear ratio of the drive gear to the driven gear is about 1:9, whereas for the second gear set, the gear ratio of the drive gear to the driven gear is about 1:1. Thus, the first output shaft, when driven by the first gear set, rotates at a slower speed as compared to the second output shaft when the latter is driven by the second gear set. As the massage drive unit travels up and down along the guiding unit, rotation of the first output shaft causes the massaging wheel unit to impart a kneading massaging action on the spine of a user seated on the chair, while rotation of the second output shaft causes the massaging wheel unit to impart a tapping massaging action on the spine of the user. The first and second one-way clutches minimize the mechanical noise that is generated as the drive shaft engages and disengages the first and second gear sets.
The main drawback of the known variable massage drive unit is as follows: The first and second one-way clutches serve to prevent the drive shaft from driving simultaneously the first and second output shafts. However, it is noted that when the massage drive unit is assembled, the drive gears of the first and second gear sets are clamped tightly between the tubular sleeve and a respective one of the upper and lower bearings. Since parts of the upper and lower bearings rotate with the drive shaft, friction between the upper and lower bearings and the drive gear of the corresponding one of the first and second gear sets will cause the latter to rotate and drive the associated driven gear and output shaft to rotate. In other words, although the first and second one-way clutches engage only one of the first and second gear sets with the drive shaft at one time, the drive shaft still drives rotatably, albeit indirectly, the other one of the first and second gear sets via the corresponding one of the upper and lower bearings. This results in improper operation of the massage drive unit.